An enzyme produced by microorganisms is used in many areas as a catalyst for chemical conversion reaction. In particular, by using nitrile hydratase, nitrilase, or the like which has an ability of hydrating or hydrolyzing a nitrile group, it is possible to produce at low cost the amides, carboxylic acids, α-hydroxycarboxylic acids or the like that are important in chemical industry. Further, by using this enzyme having an optically specific hydrating ability or an optically specific hydrolyzing ability, it is also possible to produce optically active carboxylic acids, amino acids, α-hydroxycarboxylic acids or the like that are important as a raw material for producing pharmaceuticals and agrochemicals.
For a chemical conversion reaction which uses an enzyme derived from microorganisms as a catalyst, it is necessary to preserve stably the cultured and collected micro organisms until their use. Specifically, preservation should be made such that the catalytic activity of the enzyme is not lost or lowered due to decomposition or lysis as caused by contamination. Accordingly, inactivation, decomposition, or lysis of a microbial enzyme is inhibited during the preservation of microbial cells by preserving generally in the presence of a stabilizing agent, a metabolic inhibitor, or high-concentration salts, and the enzyme is then used for a chemical conversion reaction. For a case of not adding a stabilizing agent or the like, preservation by freezing, cooling, or stirring under aeration to maintain the activity of an enzyme is known.
In case of microorganisms having nitrile hydratase activity, a method for preservation in an aqueous solution which contains inorganic salts at a high concentration (Patent Document 1), a method for preservation by freezing (Patent Document 2), a method for performing stirring under aeration with a controlled pH (Patent Document 3), or the like are known.
Meanwhile, for the purpose of enhancing convenience of a microbial catalyst user, a method for isolating solid matters after disrupting microbial cells and purifying the microbial enzyme is known (Patent Document 4).